Magneto-optical effects in transition metal systems

A theoretical description of magneto-optical effects in metallic transition metal systems on the basis of an itinerant description for the underlying electronic structure is presented and applications to the magneto-optical Kerr effect and the circular dichroism in x-ray absorption are discussed. Simple arguments based on symmetry considerations as well as electronic excitation schemes are given to show that magneto-optical effects are caused by the interplay of magnetic ordering and spin-orbit coupling. The various band structure techniques developed to deal with this situation are reviewed with an emphasize on fully relativistic methods based on the Dirac equation. The theoretical framework to calculate magneto-optical spectra on the basis of the underlying band structure is outlined in some detail. In addition, a number of sum rules derived by various authors are presented that allow one to estimate spin and orbital magnetic moments of an absorbing atom from the magnetic x-ray dichroism spectra. For the magneto-optical Kerr effect, as well as the magnetic x-ray dichroism, application of the theoretical formalism is presented for a great variety of systems, i.e. pure elements, compounds, alloys and multilayer systems. For both kinds of spectroscopies it is demonstrated that model calculations which allow one to manipulate the exchange splitting and the spin-orbit coupling strength give valuable information for a better understanding of the rather complex spectra. Concerning the sum rules, this technique together with the direct calculation of the dichroism spectra allow for a stringent test of the various assumptions on which these rules are based.